What is Pointer in C?

“Pointers are the fundamental part of C language. In embedded system programming pointer plays a major role in embedded system programming. For example dynamic memory allocation is possible only by using of pointers.  So it is necessary to understand pointers base and use it in embedded system programming”

Every variable that we declare will save on some memory location and its address is defined. This address of variable can be accessed using ampersand (&) operator. This operator will give memory address of variable.  For example:

Address1= &Value1;       // this statement assign the address of                                                  //value1 to Address1.

Here Adress1 will contain the address of Value1. Here 30 is the I value of Varaible1 and 4005 will be L value of variable.

So pointer is variable which holds the memory address of another variable. Pointers are used to access the memories and manipulate the address. Pointers play a main role in C programming. I will gives you access the memory location and manipulate them. If you want to pass a huge amount of data in to a function, it is easier to pass its address location to function then to copy every element of the  data. Moreover, if you need more memory for your program then you can allocate more memory using dynamic memory allocation.

Syntax of pointer declaration is as follows:

Data_type  *pointer_name;

Here Data_type is the type of variable for which it will be to be used. It must be as valid C data type.

“*” called as  dereference operator, this will gives you value at address. 

pointer_name will be name of the pointer.

Why data type of Pointer is required?

As we studied pointer is used to access variable using its address i.e. pointer will store the address of variables. We declare pointer according to variables data types. If we declare a pointer to integer variable data type of pointer will be integer.  The size of integer is 2 byte. It will take 16 bit to store integer value. So pointer data type of integer will be an integer. So if we access integer array of data using pointers then to access next value in any pointer increment will be of two memory location for 8-bit controllers. Same will follow for char (8-Byte) and float (4-Byte). Example of pointer declarations:

int variable1=0;                         // definition of variable1 as integer                                                    //type.        

int *pointer1=&variable1;       // integer pointer declaration  for                        //variable1 and copies the address of                  //variable1 in poiter1

char variable2=0;                    // definition of variable2 as char type.            

int *pointer2;                           // character pointer declaration  for variable1

float variable3=0;                    // definition of variable3 as float type.            

int *pointer3;                           // character pointer declaration  for variable

Accessing data using pointer

There are mainly three steps to use pointers:

1. Declaration of pointer variable
2. Assigning the address of variable to pointer variable
3. Accessing the value at address stored in pointer variable.

For example:

int data1=4, data2;                    // definition of data1 ad data2

int *pointer_to_data1;              // pointer variable definition                                                               // for data1

pointer_to_data1 = &data1;     //assigning data1 address to                                                                //poiter_to_data1

data2=*poiter_to_data1;         // this will copies the data1 value in           //data1, data2 will //contain 4